1. Field of the Invention
The present invention relates generally to the decoding of digital data. More specifically, the present invention relates to a digital circuit for decoding encoded doppler data received from a missile in flight or the like.
2. Description of the Prior Art
The pulse code modulation (PCM) or digital processing of analog data signals in the low to high frequency range is also becoming highly useful for analyzing the performance of weapons systems such as guided missiles. For example, the analog data acquired by a guided missile during flight is converted to its digital equivalent and then placed in a digital PCM frame for transmission to a ground station, a ship or an aircraft for analysis.
There are, however, some problems left unsolved in the art of digital processing of analog signals provided by a missile in flight. For, example, there is a limitation in bandwidth at which the digitized information may be transmitted from the missile to the ground station because of National Telecommunications and Information Administration frequency allocation limitations. In addition, a ground station's data receiving and processing capabilities need to be considered when transmitting pulse code modulated (PCM) flight data from a missile in flight to a ground station.
In certain applications, such as data received from a missile during flight, there is a need to increase the resolution of the equivalent digital signal provided by the missile's telemetry system. This necessitates the use of, for example, fourteen bit equivalent digital words to represent the incoming analog signal. This increase in the number of bits to represent the incoming analog signal results in a significant decrease in the error being introduced in the higher resolution bits (least significant bits) and a significant increase in the bandwidth required for transmission of the digital equivalent signal provided by the missile's telemetry system. By utilizing a form of automatic gain control (AGC) after the incoming analog signal is converted to its digital fourteen bit equivalent, a subset, for example, of four of the fourteen bits which is encoded doppler data may be transmitted with a significant increase in the accuracy and resolution of the transmitted digital information within a reduced bandwidth.
When, the encoded doppler data is received by a ground station there is a need to decode this doppler data to extract information contained in the data for the purpose of analyzing the missile's flight performance.